A Dormant Reagent Reaction‐Diffusion Method for the Generation of Co‐Fe Prussian Blue Analogue Periodic Precipitate Particle Libraries

Abstract

Liesegang patterns that develop as a result of reaction-diffusion can simultaneously form products with slightly different sizes spatially separated in a single medium. We show here a reaction-diffusion method using a dormant reagent (citrate) for developing Liesegang patterns of cobalt hexacyanoferrate Prussian Blue analog (PBA) particle libraries. This method slows the precipitation reaction and produces different-sized particles in a gel medium at different locations. The gel-embedded particles are still catalytically active. Finally, the applicability of the new method to other PBAs and 2D systems is presented. The method proves promising for obtaining similar inorganic framework libraries with catalytic abilities.

Periodic Stratification of Colloids in a Liquid Phase Produced by a Precipitation Reaction and Gel Swelling

“…However, no stratification pattern formed in the liquid phase in the case of cobalt­(II) and copper­(II) PBAs, which had micron-sized particles (Figure S9 and Movie S4). , The formation of smaller colloids can be attributed to the lower values of the solubility products of these PBAs. Iron­(III), indium­(III) ferrocyanide, and silver­(I) ferrocyanide PBAs, producing periodic stratification, have lower solubility products (3.3 × 10 –41 , 1.9 × 10 –44 , and 1.6 × 10 –41 , respectively) compared to those of cobalt­(II) ferrocyanide (1.8 × 10 –15 ) or copper­(II) ferrocyanide (1.3 × 10 –16 ) showing no pattern formation in the aqueous phase …”

“…Once a strong acid diffuses into the gel (placed on top of the gel column), the acidic environment shifts the complexation to liberate free cations that react with ferrocyanide, generating periodic precipitation in the gel. 25 This work investigates the precipitation reaction of PB and PBAs in a solid gel matrix using the DR method. 25 PB and PBAs are widely used chemical compounds to create precipitation structures in a gel matrix.…”

“…25 This work investigates the precipitation reaction of PB and PBAs in a solid gel matrix using the DR method. 25 PB and PBAs are widely used chemical compounds to create precipitation structures in a gel matrix. 26−31 In contrast to the previous studies conducted on periodic precipitation in solid gels, we observed a striking phenomenon, namely, the formation of periodic stratification of colloids in an aqueous phase above the solid hydrogel column due to the periodic swelling of the gel and long-term stability of the colloids in the aqueous phase (Figure 1c).…”

“…However, the metal cations are reversibly bonded to citrate, creating a complex (DR) that cannot react with potassium ferrocyanide to produce a precipitate. Once a strong acid diffuses into the gel (placed on top of the gel column), the acidic environment shifts the complexation to liberate free cations that react with ferrocyanide, generating periodic precipitation in the gel …”